US20060201655A1

US20060201655A1 - Heat pipe suitable for application in electronic device with limited mounting space

Info

Publication number: US20060201655A1
Application number: US11/164,325
Authority: US
Inventors: Chu-Wan Hong; Chang-Ting Lo; Jung-Yuan Wu; Ching-Tai Cheng
Original assignee: Individual
Current assignee: Foxconn Technology Co Ltd
Priority date: 2005-03-11
Filing date: 2005-11-18
Publication date: 2006-09-14
Also published as: TWI287612B; TW200632269A

Abstract

A mesh-type heat pipe (10) includes a casing (12), a tube (14) located inside the casing and a screen mesh wick (16) located between the casing and the tube. The tube defines therein a plurality of through holes (142) and at least one cutout (144). The wick is held against the casing by the tube. Under the support of the tube, the wick as a whole engages closely an inner surface of the casing, thereby establishing an effective heat transfer path between the casing and a working fluid that is saturated in the wick. Meanwhile, with the cutout in the tube presented, the heat pipe incorporating such tube is easily to be bent or flattened so as to enable the heat pipe to be applicable in electronic devices with a limited mounting space for a cooling device, such as notebook computers.

Description

FIELD OF THE INVENTION

The present invention relates generally to an apparatus for transfer or dissipation of heat from heat-generating components such as electronic components, and more particularly to a heat pipe that is suitable for use in electronic devices that have a limited mounting space, such as notebook computers.

DESCRIPTION OF RELATED ART

Heat pipes have excellent heat transfer performance due to their low thermal resistance, and therefore are an effective means for transfer or dissipation of heat from heat sources. Currently, heat pipes are widely used for removing heat from heat-generating components such as central processing units (CPUs) of computers. A heat pipe is usually a vacuum casing containing therein a working fluid, which is employed to carry, under phase transitions between liquid state and vapor state, thermal energy from one section of the heat pipe (typically referring to as “evaporating section”) to another section thereof (typically referring to as “condensing section”). Preferably, a wick structure is provided inside the heat pipe, lining an inner wall of the casing, for drawing the working fluid back to the evaporating section after it is condensed at the condensing section. Specifically, as the evaporating section of the heat pipe is maintained in thermal contact with a heat-generating component, the working fluid contained at the evaporating section absorbs heat generated by the heat-generating component and then turns into vapor. Due to the difference of vapor pressure between the two sections of the heat pipe, the generated vapor moves towards and carries the heat simultaneously to the condensing section where the vapor is condensed into liquid after releasing the heat into ambient environment by, for example, fins thermally contacting the condensing section. Due to the difference of capillary pressure developed by the wick structure between the two sections, the condensed liquid is then drawn back by the wick structure to the evaporating section where it is again available for evaporation.
The wick structure currently available for the heat pipe includes fine grooves integrally formed at the inner wall of the casing, screen mesh or bundles of fiber inserted into the casing and held against the inner wall thereof, or sintered powder combined to the inner wall of the casing by sintering process. As for the screen mesh wick, its manufacture generally involves weaving together a plurality of pliable wires or threads such as metal wires or synthetic fibers. In this sense, the screen mesh wick is formed separately and is then inserted into the casing of the heat pipe.
In the heat pipe, except the function to generate capillary force for drawing the condensed liquid back to the evaporating section of the heat pipe, another function of the wick structure is to provide a heat transfer path between the casing of the heat pipe and the working fluid that is contained in the casing and saturated in the wick structure. Therefore, whether the wick is maintained into intimate contact with the casing will have a great impact on the heat transfer effect of the heat pipe. However, since the screen mesh wick is made separately, in many cases a gap will exist between the screen mesh wick and the casing of the heat pipe after the screen mesh wick is inserted into the heat pipe. In order to hold the screen mesh wick against and ultimately into close contact with the casing of the heat pipe, retaining means are often used. For example, a helical spring or a round tube will generally serve this purpose. The helical spring is not satisfactory in holding the screen mesh wick against the casing of heat pipe since it generally cannot apply a uniform force on the wick for pressing it against the casing due to a limited contact area between the spring and the wick.
In many cases, a heat pipe is required to be bent into a curved one or pressed into a flattened one in order to be applicable in electronic devices that have very limited mounting space, for example, in some portable electronic devices such as notebook computers. Although the round tube could provide a more uniform pressing force for the wick in comparison to the helical spring, the tube generally is made of rigid material such as metals and therefore adds difficulty to the bending or flattening work, since the rigidity of the tube has to be overcome in order to bend or flatten the heat pipe.
Therefore, it is desirable to provide a retaining means for the screen mesh wick that could apply a uniform pressing force for the wick and meantime make the bending or flattening work to the heat pipe, if necessary, more easier.

SUMMARY OF INVENTION

A heat pipe in accordance with one embodiment of the present invention includes a casing, a tube located inside the casing and a screen mesh wick located between the casing and the tube. The tube defines therein a plurality of through holes and at least one cutout. The wick is held against the casing by the tube. Under the support of the tube, the wick as a whole engages closely an inner surface of the casing, thereby establishing an effective heat transfer path between the casing and a working fluid that is saturated in the wick. Meanwhile, with the cutout in the tube presented, the heat pipe incorporating such tube is easily to be bent or flattened so as to enable the heat pipe to be applicable in electronic devices with limited mounting space for cooling device, such as notebook computers.
Other advantages and novel features of the present invention will become more apparent from the following detailed description of preferred embodiment when taken in conjunction with the accompanying drawings, in which:

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a longitudinal cross-sectional view of a heat pipe in accordance with a first embodiment of the present invention;
FIG. 2 is an isometric view of the heat pipe of FIG. 1, showing various parts thereof in the assembly process;
FIG. 3 is a side elevation view of a tube suitable for the heat pipe of FIG. 1, according to a second embodiment of the present invention;
FIG. 4 is a side elevation view of a tube suitable for the heat pipe of FIG. 1, according to a third embodiment of the present invention; and
FIG. 5 is a cross-sectional view of the tube of FIG. 4, taken along line V-V thereof.

DETAILED DESCRIPTION

FIG. 1 illustrates a heat pipe 10 in accordance with one embodiment of the present invention. The heat pipe 10 includes a casing 12, a tube 14 inserted into the casing 12 and a capillary wick 16 located between the casing 12 and the tube 14. The wick 16 is held by the tube 14 to engage closely an inner surface of the casing 12. The casing 12 is typically made of high thermally conductive materials such as copper or copper alloys. Although the casing 12 as illustrated is in a round shape, it should be recognized that other shapes, such as rectangle or the like, may also be suitable. The wick 16 is a screen mesh wick having a porous structure and is saturated with a working fluid (not shown), which acts as a heat carrier for carry thermal energy inside the heat pipe 10 when undergoing a phase transition from liquid state to vaporous state. The working fluid is usually selected from liquids such as water or alcohol and is compatible with the wick 16, the tube 14 and the casing 12.
The screen mesh wick 16 is typically made independently of the casing 12 by weaving together a plurality of flexible wires or threads such as metal wires or synthetic fibers. Then the wick 16 is rolled and inserted into the casing 12. The tube 14 is capable of applying a uniform pressing force on the wick 16 in order to maintain the wick 16 as a whole into close contact with the casing 12, thus providing an effective heat transfer path between the casing 12 and the working fluid saturated in the wick 16. The tube 14 defines therein a plurality of through holes 142 through its inner and outer surfaces thereof. These through holes 142 are round in shape, although other shapes such as rectangle or triangle or the like may also be suitable. In addition, the through holes 142 may be arranged at the tube 14 regularly or irregularly. The design of the through holes 142 is to enable a communication of the working fluid between the wick 16 and a hollow vapor channel (not labeled) defined in the casing 12 and the tube 14. Specifically, when the working fluid contained in the wick 16 receives heat from a heat source in thermal connection with an evaporating section (not labeled) of the heat pipe 10 and turns into vapor, the vapor goes into the vapor channel defined by the casing 12 via the through holes 142 and then moves, through the vapor channel, toward a condensing section (not labeled) of the heat pipe 10 where the vapor releases its heat and turns into liquid. Then, the condensed liquid returns from the vapor channel into the wick 16 again via the through holes 142. Thereafter, the liquid is drawn back to the evaporating section of the heat pipe 10 via the wick 16 where it is available again for evaporation. The through holes 142, preferably, account for about 70 percents of a total surface area of the tube 14 so as to enable the vapor to go into the vapor channel and the liquid to return back the wick 16 smoothly. In this situation, however, the tube 14 is still capable of providing enough support for the wick 16.
In order for the heat pipe 10 to be suitable for use in electronic devices such as notebook computers where the heat pipe 10 is usually required to be in a curved or flattened configuration due to limited mounting space inside these electronic devices, the tube 14 defines therein a cutout 144 along a circumferential direction thereof. The cutout 144 is elongated. The cutout 144 extends through a large portion of a circumferential periphery of the tube 14, but does not cut the tube 14 into two pieces. Due to the existence of the cutout 144, the heat pipe 10 is easily to be bent into a curved configuration from the location where the cutout 144 is located, without the necessity of overcoming the rigidity of the tube 14 especially if the tube 14 is made of rigid material such as metals. Although in this embodiment the cutout 144 forms a right angle with respect to an axis (not labeled) of tube 14, it should be recognized that in some other circumstances the cutout 144 may also be defined slantwise in the tube 14 and in doing so, an acute angle is formed between the cutout 144 thus defined and the axis of the tube 14. It should also be recognized that if the heat pipe 10 is needed to be bent in more than one location, more than one cutout 144 may be formed in the tube 14. The tube 14 may be made of metals such as copper or aluminum, and in order to reduce the rigidity of the tube 14, organic material such as polyethylene, polycarbonate, polyamide, or the like may also be suitable for the tube 14.
As shown in FIG. 2, in assembly, the wick 16 which is typically made by weaving technology is firstly wrapped around on the tube 14. The tube 14 may be manufactured by pressing or forging or injection molding to form firstly a flat plate with the through holes 142 formed therein and then rolling the flat plate into the tube 14. Then, the tube 14, together with the wick 16 wrapped therearound, is inserted into the casing 12 after the casing 12 is heated to expand with a required extent. As the casing 12 is cooled down to its original size, the wick 16 is thereby tightly and evenly held against the inner surface of the casing 12 under the support of the tube 14.
FIG. 3 illustrates a tube 14 a according to a second embodiment of the present invention. Compared with the above-mentioned first embodiment, the tube 14 a is divided into two separate pieces by an elongated cutout 145 transversely cutting through the tube 14 a.
FIGS. 4-5 illustrate a tube 14 b according to a third embodiment of the present invention. The tube 14 b defines therein a pair of opposite elongate cutouts 146 along a longitudinal direction thereof. Each cutout 146 has two sections (not labeled) extending from opposite ends of the tube 14 b till a middle thereof. The two sections do not communicate with each other. In the presence of the cutouts 146, this tube 14 b is typically suitable for use in heat pipes that need to be pressed into flattened configurations.
According to the above-mentioned embodiments, each of the tubes is capable of providing a uniform pressing force against the wick of the heat pipe so as to maintain the wick into intimate contact with the casing of the heat pipe, thereby establishing an effective heat transfer path between the casing and the working fluid saturated in the wick. Meanwhile, with the cutouts in the tubes presented, the heat pipes incorporating such tubes are easier to be bent or flattened in order to be applicable in modern electronic devices having a limited mounting space for a cooling device.
It is to be understood, however, that even though numerous characteristics and advantages of the present invention have been set forth in the foregoing description, together with details of the structure and function of the invention, the disclosure is illustrative only, and changes may be made in detail, especially in matters of shape, size, and arrangement of parts within the principles of the invention to the full extent indicated by the broad general meaning of the terms in which the appended claims are expressed.

Claims

1. A heat pipe comprising:

a casing;

a tube located inside the casing, the tube defining therein a plurality of through holes and at least one cutout; and

a screen mesh wick located between the casing and the tube and held by the tube against the casing.

2. The heat pipe of claim 1, wherein the at least one cutout extends along one of circumferential and longitudinal directions of the tube.

3. The heat pipe of claim 1, wherein the tube is divided into multiple separate pieces by the at least one cutout.

4. The heat pipe of claim 1, wherein the tube is made of one of organic material and metal material.

5. The heat pipe of claim 1, wherein the through holes account for 70 percent of a total surface area of the tube.

6. The heat pipe of claim 1, wherein the screen mesh wick is made of a plurality of flexible wires by weaving technology.

7. A method for manufacturing a heat pipe comprising steps of:

providing a tube with a plurality of through holes and at least one cutout defined therein;

wrapping a screen mesh wick onto an outer surface of the tube; and

inserting the tube and the wick into a hollow casing.

8. The method of claim 7, wherein the tube and the wick are inserted into said casing after said casing is heated to expand with a required extent.

9. The method of claim 7, wherein the screen mesh wick is made of a plurality of flexible wires by weaving technology.

10. The method of claim 7, wherein the at least one cutout is formed along one of circumferential and longitudinal directions of the tube.

11. The method of claim 7, wherein the tube is made of one of organic material and metal material.

12. A heat pipe for transferring heat from one section to another section thereof, comprising:

a metal casing having an inner surface defining a hollow space therein;

a screen mesh wick contacting the inner surface of the metal casing; and

a tube received in the hollow space and pressing the wick against the inner surface of the metal casing, wherein the tube defines a plurality of holes therethrough and at least one elongated cutout therein.

13. The heat pipe of claim 12, wherein the at least one cutout is defined in the tube along a circumferential direction thereof.

14. The heat pipe of claim 13, wherein the at least one cutout extends all through the tube and divides the tube into two pieces.

15. The heat pipe of claim 13, wherein the least one cutout is perpendicular to an axis of the tube.

16. The heat pipe of claim 13, wherein the at least one cutout is slanted to an axis of the tube.

17. The heat pipe of claim 12, wherein the at least one cutout is defined in the tube along a longitudinal direction thereof.

18. The heat pipe of claim 17, wherein the at least one cutout comprises two sections extending from two opposite ends of the tube toward a middle thereof.

19. The heat pipe claim 17, wherein the tube comprises an additional cutout extending along the longitudinal direction thereof and located opposite the at least one cutout.

20. The heat pipe of claim 19, wherein each of the at least one cutout and the additional cutout comprises two sections extending from two opposite ends of the tube toward a middle thereof.